This invention relates to optoelectronic devices used to measure the rotational speed of a rotating shaft, and more particularly to optoelectronic devices used to measure the rotational speed of a shaft of a turbosupercharger installed on an internal combustion engine.
For the design and optimization of internal combustion engines which have turbosuperchargers installed on them, it is necessary to measure the rotational speed of the turbosupercharger shaft because conclusions can be drawn from these measurements related to the response behavior of the turbosupercharger, which is directly related to the power behavior of the internal combustion engine itself.
In automotive engineering, inductive pulse generators are as a rule used for measuring the speed of shafts. "Bosch Technische Berichte" (Bosch Technical Reports), Volume 7 (1981), Issue 3, Page 140-141, shows such a pulse generator that is designed as a passive magnetic stray field sensor. These pulse generators operate on the theory that on at least part of the shaft ferromagnetic "marks" exist or may be mounted, such as the steel teeth on the toothed rim of the flywheel disk, or a steel or iron pin placed in a rotating part of an internal combustion engine.
It is possible to measure the speed of the shaft of the turbosupercharger by means of such a pulse generator mounted in the turbosupercharger housing by counting the charging wheel blades passing the pulse generator per time unit. However, since the blades of a turbosupercharger generally are formed from materials which are either non-ferromagnetic or are otherwise unsuitable for providing sufficient magnetic return, turbosuperchargers to be so measured must be constructed correspondingly by providing them with ferromagnetic "marks" on the charger wheel. This results in increased costs and problems with balance errors. In addition, in turbosuperchargers high temperatures (up to about 280.degree.) normally occur, especially after the internal combustion engine is shut off, which can damage the insulating materials of the pulse generator.
Further problems with pulse generators are caused by components of the commonly used high-capacity ignition systems being located in direct proximity to the turbosuperchargers since the pulse generators are sensitive to high value stray electromagnetic fields. The resulting interferences can not be filtered out of the measuring signal.
Still further problems with pulse generators are caused by the requirement for exact positioning of the pulse generators in such a highly stressed part of the internal combustion engine.
An apparatus for measuring the rotational speed of a vehicle wheel is known from DE-OS No. 3,036,846 (German Published Unexamined Patent Application). That apparatus locates the temperature-sensitive and shock-sensitive electronic system for the signal regeneration and processing about 10 cm away from the speed sensor on the vehicle wheel. The speed sensor and electronic signal processing system are connected via electric leads or optical-guide cables. Although this apparatus does allow the most temperature-sensitive and shock-sensitive components to be located away from the measuring point, the speed sensor is still located in a dangerous area. The speed sensor is then connected with the electronic processing system via a connecting lead that is insensitive to temperature and secure with respect to stray fields.
One disadvantage of this type of system is that the connecting lead between the speed sensor and the electronic processing system is generally only 10 cm to 15 cm in length. This length is too short for a turbosupercharger application because the electronic system would have to be located in an area which is continuously subjected to high temperatures and high capacitive and electromagnetic stray fields. For a turbosupercharger application it is desirable that the entire electronic processing system be located in a measuring area of an internal combustion engine testing stand or in the area of the dashboard of a motor vehicle to be tested.
Another disadvantage of this type of system is the requirement for a special modulator which cannot be mounted on the shaft of a turbosupercharger or can only be mounted with great difficulty. These modulators require high finishing accuracy, an exact concentricity, and a precise centering during the mounting which makes them expensive.
One objective of the present invention is to provide an apparatus for the optoelectronic measuring of the rotational speed of a shaft such that the apparatus can be not only mounted easily, but is also isolated from, and insensitive to, shock, high temperatures, and relatively strong electromagnetic and capacitive stray fields.
According to the present invention, an optoelectronic measuring device is provided which can measure the rotational speed of a shaft, and more particularly the rotational speed of a turbosupercharger shaft where the turbosupercharger is a part of an internal combustion engine. The measuring device is able to function without a special modulator and without the restriction of a short connecting lead between the sensor unit and the receiving unit. This permits the mounting of only the sensor unit to the turbosupercharger which requires no significant structural changes while the receiving unit may be located in a convenient area some distance away. This mounting method permits the acquisition and processing of interference free signals and further permits the apparatus to be manufactured in a simple and cost efficient manner.
Further objects, features and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, an embodiment in accordance with the present invention.